Microbioluminometry assay: determination of erythromycin activity in plasma or serum

A microbioluminometry assay (MBA) was developed for the quantitative analysis of erythromycin activity in human plasma or serum. The MBA method is adapted from turbidimetric methods and utilizes an enzyme-catalyzed bioluminescence reaction to quantitate the growth of Staphylococcus aureus in liquid culture medium. Statistical analysis of data obtained in method validation studies and in more than 500 assays of standard curve and control samples demonstrates consistent reproducibility and accuracy within theoretical limits. The MBA was shown to be more sensitive than agar diffusion assays with a lower limit of sensitivity less than 20.0 ng/mL and coefficients of variation less than 10%. Cumulative results of 178 assays of spiked control plasma samples in the range of 0.14-2.18 micrograms/mL show 11.2% of individual determinations are greater than +/- 15% the expected value, and 5.6% of individual determinations are greater than +/- 20% the expected value. Bioavailability profiles obtained with MBA are consistent with reported data for erythromycin. Values for 206 subject samples analyzed by MBA and agar diffusion assays showed a high degree of correlation (r = 0.9525) between the two methods. The MBA technique provided high sample throughput because of the use of microtiter plate technologies; it is also economical since it requires less sample and reagents.